The present invention relates to a method of forming a minute resist pattern wherein a resist pattern with high sensitivity, high resolution, and an excellent film retention rate can be obtained by use of a positive-working photoresist composition.
Heretofore, a method of forming a minute resist image on a substrate by applying a positive-working photoresist composition to a substrate to form a resist film, exposing it with radiation such as UV rays, deep UV rays, X rays and electron beams and then developing the resist film, that is, the formation of a minute resist pattern by the photolithography method is well-known. In this photolithography method using the positive-working photoresist composition, 2.38 to 2.50 weight % aqueous tetramethyl ammonium hydroxide or 0.50 weight % or more aqueous sodium hydroxide or potassium hydroxide is used as the developing solution. On the other hand, as the positive-working photoresist composition, a composition comprising an alkali-soluble resin and a quinone diazide group-containing photosensitizer, for example a naphthoquinone diazide-type compound is conventionally and generally used. The positive-working photoresist composition using a novolak-type phenol resin as the alkali-soluble resin and a substituted naphthoquinone diazide compound as the photosensitizer is described in, for example, U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. In these known positive-working photoresist compositions, the naphthoquinone diazide-type compound as the photosensitizer is used in an amount of usually 15 parts by weight or more, frequently 20 to 30 parts by weight relative to 100 parts by weight of the novolak-type phenol resin. However, when these known positive-working photoresist compositions are used as a photoresist composition and developed with the above-described known developing solution as a developing solution, the high sensitive photoresist particularly for TFT (thin film transistor) indicates poor film retention rate (due to too much reduction in film thickness), so there is near limit to attempt for further improvements insensitivity of the photoresist. In addition, there arises another problem of high process dependency, that is, the characteristics of resist patterns formed vary significantly when treatment conditions in treatment processes are varied (accordingly, process tolerance is reduced).
For the purpose of conferring high sensitivity on the photoresist, it has been attempted to increase the concentration of an alkali in the developing solution or to prolong the developing time. However, if the concentration of an alkali in the developing solution is increased, the resist on unexposed areas shows significantly poor film retention rate, thus failing to attain sufficient resistance in the subsequent etching step, while if the development time is prolonged, there arises the problem of failing to achieve a sufficient effect on the so-called through-put (treatment efficiency per unit time). Further, it is also proposed to add various low-molecular components as the sensitizer. In this case, sensitivity can be improved, but the unexposed portion is easily dissolved in a developing solution together with an exposed area, resulting in a significant reduction in the film retention rate.
On the other hand, for the purpose of improving the resolution of the resulting resist patterns, it has been proposed to add a wide variety of additives such as surface active agents and organic compounds. Such photoresist compositions comprising surface active agents include those described in Japanese Patent Application Laid-Open (JP-A) Nos. 61-70551, 61-151537, 61-232454 and 62-32454, and those compositions comprising other organic compounds such as hydrocarbons in addition to surface active agents include those described in e.g. JP-A No. 62-232453. These compositions have both advantages and disadvantages, and none of these satisfy practically all of high resolution, high film retention rate and high dimension accuracy.
Under the circumstances described above, the object of the present invention is to provide a positive-working photoresist composition, a developing solution and a photolithography method comprising a combination thereof which can simultaneously achieve high sensitivity, a high film retention rate, high resolution, low process dependency, and a formation of excellent pattern profile, that is, can achieve high sensitivity while maintaining a high film retention rate and can form good patterns having high resolution and low dependency of dimensional accuracy in a photolithography method using a positive-working photoresist.
As a result of their eager study and examination, the present inventors found that the object described above can be achieved by a combination of a specific positive-working photoresist composition and a specific developing solution, thus completing the present invention.
That is, the present invention relates to a method of forming a minute resist pattern by use of a positive-working photoresist composition, wherein a photoresist composition comprising 3 to 15 parts by weight of a quinone diazide group-containing photosensitizer relative to 100 parts by weight of alkali-soluble novolak resin is used as the positive-working photoresist composition, and an aqueous organic or inorganic alkali solution having a lower alkali concentration than that of the conventional one is used as the developer.
In the present invention, as the developing solution, 2.2% by weight or less of an aqueous solution of a quaternary ammonium hydroxide represented by the general formula (1):
xe2x80x83[(R1)3Nxe2x80x94R2]+OHxe2x88x92xe2x80x83xe2x80x83(1)
wherein R1 represents an alkyl group having 1 to 3 carbon atoms, and R2 represents an alkyl group having 1 to 3 carbon atoms or a hydroxy-substituted alkyl group having 1 to 3 carbon atoms, or 0.4% by weight or less of an aqueous solution of an inorganic hydroxide represented by the general formula (2):
MOHxe2x80x83xe2x80x83(2)
wherein M represents an alkali metal.
In the present invention, preferable examples of quaternary ammonium compounds represented by the general formula (1) above include tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, trimethylethyl ammonium hydroxide, trimethyl(2-hydroxyethyl)ammonium hydroxide, triethyl(2-hydroxyethyl)ammonium hydroxide, tripropyl(2-hydroxyethyl)ammonium hydroxide and trimethyl(2-hydroxypropyl)ammonium hydroxide. Particularly preferable examples among these are tetramethyl ammonium hydroxide (referred to hereafter as xe2x80x9cTMAHxe2x80x9d) and trimethyl(2-hydroxyethyl)ammonium hydroxide (choline). Particularly preferable examples of inorganic hydroxides represented by the general formula (2) above are sodium hydroxide and potassium hydroxide.
To confer a buffering effect, the developing solution may contain carbonates or bicarbonates such as those of sodium or potassium as necessary. For the purpose of raising the permeability of the developing solution, surface active agents may also be contained therein.
Development with the developing solution of this invention may be conducted in any methods known in the art, such as immersion, spraying and paddling. The temperature, time etc. at the development may be suitably determined depending on the type of the photoresist composition used and the development method used.
The alkali-soluble novolak resin in the positive-working photoresist composition used in this invention is obtained by polycondensation of various phenols with aldehydes such as formaldehyde.
The phenols used include e.g. phenol, p-cresol, m-cresol, o-cresol, 2,3-dimethyl phenol, 2,4-dimethyl phenol, 2,5-dimethyl phenol, 2,6-dimethyl phenol, 3,4-dimethyl phenol, 3,5-dimethyl phenol, 2,3,4-trimethyl phenol, 2,3,5-trimethyl phenol, 3,4,5-trimethyl phenol, 2,4,5-trimethyl phenol, methylene bisphenol, methylene bis-p-cresol, resorcin, catechol, 2-methyl resorcin, 4-methyl resorcin, o-chlorophenol, m-chlorophenol, p-chlorophenol, 2,3-dichlorophenol, m-methoxyphenol, p-methoxyphenol, p-butoxyphenol, o-ethyl phenol, m-ethyl phenol, p-ethyl phenol, 2,3-diethyl phenol, 2,5-diethyl phenol, p-isopropyl phenol, xcex1-naphthol and xcex2-naphthol. These phenol compounds can be used alone or as a mixture thereof.
As the aldehydes, not only formaldehyde but also paraformaldehyde, acetaldehyde, benzaldehyde, hydroxybenzaldehyde, chloroacetaldehyde and the like can be used alone or as a mixture thereof.
The quinone diazide group-containing photosensitizer of the present invention may be any known one, and preferable examples include those produced by allowing naphthoquinone diazidosulfonic acid chloride or benzoquinone diazidosulfonic acid chloride to react with a low- or high-molecular compound containing a functional group capable of condensation reaction with acid chloride. The functional group capable of condensation reaction with the acid chloride includes a hydroxyl group, an amino group etc., among which a hydroxyl group is particularly preferable. The low-molecular compound containing hydroxyl group(s) includes e.g. hydroquinone, resorcin; polyhydroxybenzophenones such as 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4,6-trihydroxybenzophenone, 2,4,4xe2x80x2-trihydroxybenzophenone, 2,3,4,4xe2x80x2-tetrahydroxybenzophenone, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone and 2,2xe2x80x2,3,4,6xe2x80x2-pentahydroxybenzophenone; bis((poly)hydroxyphenyl)alkanes such as bis(2,4-dihydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane and bis(2,4-dihydroxyphenyl)propane-1; and polyhydroxytriphenylmethanes such as 4,4xe2x80x2,3xe2x80x3,4xe2x80x3-tetrahydroxy-3,5,3xe2x80x2,5xe2x80x2-tetramethyltriphenylmethane, 4,4xe2x80x2,2xe2x80x3,3xe2x80x3,4xe2x80x3-pentahydroxy-3,5,3xe2x80x2,5xe2x80x2-tetramethyltriphenylmethane, and 2,3,4,2xe2x80x2,3xe2x80x2,4xe2x80x2,3xe2x80x3,4xe2x80x3-octahydroxy-5,5xe2x80x2-diacetyltriphenylmethane, while the high-molecular compound containing hydroxyl group(s) includes e.g. novolak resin, polyhydroxystyrene etc.
In the present invention, the proportion of the alkali-soluble novolak resin and the quinone diazide-containing photosensitizer is selected such that the latter is 3 to 15 parts by weight relative to 100 parts of the former.
If the amount of the latter is less than 3 parts by weight, the film retention rate after development with the low-conc. alkali developing solution of this invention is significantly lowered. On the other hand, if it is larger than 15 parts by weight, the film retention rate is improved, but the sensitivity is decreased. Therefore it is not practical. There is a quantitative relationship for maximizing the characteristics of the photoresist composition between the number of parts of the photosensitizer relative to the number of parts of the novolak resin and the concentration of the developing solution used therefor.
The solvent in which the alkali-soluble novolak resin and the photosensitizer in the present invention are dissolved includes ethylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; ethylene glycol monoalkyl ether acetates such as ethylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether and propylene glycol monoethyl ether; propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; lactates such as methyl lactate and ethyl lactate, aromatic hydrocarbons such as toluene and xylene; ketones such as methyl ethyl ketone, 2-heptanone and cyclohexanone; amides such as N,N-dimethylacetamide and N-methylpyrrolidone; and lactones such as xcex3-butyrolactone. These solvents are used singly or as a mixture thereof.
The positive-working photoresist composition of this invention can contain known additives such as dyestuffs, adhesive aids and surface active agents as necessary.
The dyestuffs include e.g. Methyl Violet, Crystal Violet, Malachite Green etc.; the adhesive aids include e.g. alkyl imidazoline, butyric acid, alkyl acid, polyhydroxystyrene, polyvinylmethyl ether, t-butyl novolak, epoxy silane, epoxy polymer, silane etc.; and the surface active agents include e.g. nonionic surface active agents such as polyglycols and derivatives thereof, that is, polypropylene glycol or polyoxyethylene lauryl ether, fluorine-containing surface active agents such as Fluorad (Sumitomo 3M Ltd.), Megafac (Dainippon Ink and Chemicals, Inc.), Sulflon (Asahi Glass Co., Ltd.) or organic siloxane surface active agents such as KP341 (Shin-Etsu Chemical Co., Ltd.).